ObjectivesMalnutrition, particularly protein insufficiency, is common in institutionalised older adults and increases morbidity, mortality, and costs. We aimed to determine whether 12 months supplementation using high-protein foods (milk, cheese, yoghurt) prevents malnutrition in older adults.DesignCluster randomised control study.SettingSixty Australian aged care facilities.ParticipantsOlder adults living in aged care homes (n=654, mean age 86.7±7.2 years, 72% females).InterventionFacilities randomly allocated to a high-protein (n=30 intervention) or regular (n=30 controls) menu.MeasurementsNutritional status assessed using the Mini Nutrition Assessment (MNA) tool and fasting morning blood samples (n=302) assayed for haemoglobin (Hb) and albumin. Food intake was monitored 3-monthly using visual plate waste assessment. Measurements at baseline and month 12 were analysed using random effects model accounting for clustering (facility), repeated measure and confounders.ResultsAddition of 11g of protein as 1.5 servings of high-protein foods daily preserved nutritional status that deteriorated in controls [MNA screen (−0.68, 95%CI: −1.03, −0.32, p<0.001) and total (−0.90, 95%CI: −1.45, −0.35, p=0.001) scores], resulting in group differences in MNA screen (0.62, 95%CI: 0.17, 1.06, p=0.007) and total (0.81, 95%CI: 0.11, 1.51, p=0.023) scores and group difference in Hb (3.60g/L, 95%CI: 0.18, 7.03, p=0.039), the net result of preservation with intervention (0.19g/L, 95%CI: −2.04, 2.42, p=0.896) and a decline in controls (−3.41g/L, 95%CI: −6.01, −0.82, p=0.010). No group differences were observed for serum albumin.ConclusionConsumption of high-protein foods is a pragmatic approach to maintaining nutritional status in older adults in aged-care.